19,965 research outputs found
Review of small-angle coronagraphic techniques in the wake of ground-based second-generation adaptive optics systems
Small-angle coronagraphy is technically and scientifically appealing because
it enables the use of smaller telescopes, allows covering wider wavelength
ranges, and potentially increases the yield and completeness of circumstellar
environment - exoplanets and disks - detection and characterization campaigns.
However, opening up this new parameter space is challenging. Here we will
review the four posts of high contrast imaging and their intricate interactions
at very small angles (within the first 4 resolution elements from the star).
The four posts are: choice of coronagraph, optimized wavefront control,
observing strategy, and post-processing methods. After detailing each of the
four foundations, we will present the lessons learned from the 10+ years of
operations of zeroth and first-generation adaptive optics systems. We will then
tentatively show how informative the current integration of second-generation
adaptive optics system is, and which lessons can already be drawn from this
fresh experience. Then, we will review the current state of the art, by
presenting world record contrasts obtained in the framework of technological
demonstrations for space-based exoplanet imaging and characterization mission
concepts. Finally, we will conclude by emphasizing the importance of the
cross-breeding between techniques developed for both ground-based and
space-based projects, which is relevant for future high contrast imaging
instruments and facilities in space or on the ground.Comment: 21 pages, 7 figure
Hybrid visual servoing with hierarchical task composition for aerial manipulation
© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper a hybrid visual servoing with a hierarchical task-composition control framework is described for aerial manipulation, i.e. for the control of an aerial vehicle endowed with a robot arm. The proposed approach suitably combines into a unique hybrid-control framework the main benefits of both image-based and position-based control schemes. Moreover, the underactuation of the aerial vehicle has been explicitly taken into account in a general formulation, together with a dynamic smooth activation mechanism. Both simulation case studies and experiments are presented to demonstrate the performance of the proposed technique.Peer ReviewedPostprint (author's final draft
Structure and Composition of Molecular Clouds with CN Zeeman Detections I: W3OH
We have carried out a multi-species study of a region which has had previous
measurements of strong magnetic fields through the CN Zeeman effect in order to
to explore the relationship between CN and NH, both of which have
evidence that they remain in the gas phase at densities of 10 - 10
cm. To achieve this we map the 1 arcmin region around the UCHII
region of W3(OH) using the Combined Array for Millimeter-wave Astronomy
(CARMA). Approximately 105 hours of data were collected in multiple array
configurations to produce maps with an effective resolution of
2.5\arcsec at high signal-to-noise in CN, CO, HCN, HCO, NH,
and two continuum bands (91.2 GHz and 112 GHz). These data allow us to compare
tracer molecules associated with both low and high density regions to infer gas
properties. We determine that CARMA resolves out approximately 35% of the CN
emission around W3(OH) when compared with spectra obtained from the IRAM-30
meter telescope. The presence of strong absorption lines towards the continuum
source in three of the molecular transitions infers the presence of a cold,
dark, optically thick region in front of the continuum source. In addition, the
presence of high-velocity emission lines near the continuum source shows the
presence of hot clumpy emission behind the continuum source. These data
determine that future high-resolution interferometric CN Zeeman measurements
which cannot currently be performed (due to technical limitations of current
telescopes) are feasible. We confirm that CN is indeed a good tracer for high
density regions; with certain objects such as W3(OH) it appears to be a more
accurate tracer than NH.Comment: 33 pages, 16 figures. Accepted by Ap
3D Visual Perception for Self-Driving Cars using a Multi-Camera System: Calibration, Mapping, Localization, and Obstacle Detection
Cameras are a crucial exteroceptive sensor for self-driving cars as they are
low-cost and small, provide appearance information about the environment, and
work in various weather conditions. They can be used for multiple purposes such
as visual navigation and obstacle detection. We can use a surround multi-camera
system to cover the full 360-degree field-of-view around the car. In this way,
we avoid blind spots which can otherwise lead to accidents. To minimize the
number of cameras needed for surround perception, we utilize fisheye cameras.
Consequently, standard vision pipelines for 3D mapping, visual localization,
obstacle detection, etc. need to be adapted to take full advantage of the
availability of multiple cameras rather than treat each camera individually. In
addition, processing of fisheye images has to be supported. In this paper, we
describe the camera calibration and subsequent processing pipeline for
multi-fisheye-camera systems developed as part of the V-Charge project. This
project seeks to enable automated valet parking for self-driving cars. Our
pipeline is able to precisely calibrate multi-camera systems, build sparse 3D
maps for visual navigation, visually localize the car with respect to these
maps, generate accurate dense maps, as well as detect obstacles based on
real-time depth map extraction
Hierarchical structure-and-motion recovery from uncalibrated images
This paper addresses the structure-and-motion problem, that requires to find
camera motion and 3D struc- ture from point matches. A new pipeline, dubbed
Samantha, is presented, that departs from the prevailing sequential paradigm
and embraces instead a hierarchical approach. This method has several
advantages, like a provably lower computational complexity, which is necessary
to achieve true scalability, and better error containment, leading to more
stability and less drift. Moreover, a practical autocalibration procedure
allows to process images without ancillary information. Experiments with real
data assess the accuracy and the computational efficiency of the method.Comment: Accepted for publication in CVI
Calibration and evaluation of optical systems for full-field strain measurement
The design and testing of a reference material for the calibration of optical systems for strain measurement is described, together with the design and testing of a standardized test material that allows the evaluation and assessment of fitness for purpose of the most sophisticated optical system for strain measurement. A classification system for the steps in the measurement process is also proposed and allows the development of a unified approach to diagnostic testing of components or sub-systems in an optical system for strain measurement based on any optical technique. The results described arise from a European study known as SPOTS whose objectives were to begin to fill the gap caused by a lack of standards
VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit
HR8799 is orbited by at least four giant planets, making it a prime target
for the recently commissioned Spectro-Polarimetric High-contrast Exoplanet
REsearch (VLT/SPHERE). As such, it was observed on five consecutive nights
during the SPHERE science verification in December 2014. We aim to take full
advantage of the SPHERE capabilities to derive accurate astrometric
measurements based on H-band images acquired with the Infra-Red Dual-band
Imaging and Spectroscopy (IRDIS) subsystem, and to explore the ultimate
astrometric performance of SPHERE in this observing mode. We also aim to
present a detailed analysis of the orbital parameters for the four planets. We
report the astrometric positions for epoch 2014.93 with an accuracy down to 2.0
mas, mainly limited by the astrometric calibration of IRDIS. For each planet,
we derive the posterior probability density functions for the six Keplerian
elements and identify sets of highly probable orbits. For planet d, there is
clear evidence for nonzero eccentricity (), without completely
excluding solutions with smaller eccentricities. The three other planets are
consistent with circular orbits, although their probability distributions
spread beyond , and show a peak at for planet e. The
four planets have consistent inclinations of about with respect to the
sky plane, but the confidence intervals for the longitude of ascending node are
disjoint for planets b and c, and we find tentative evidence for
non-coplanarity between planets b and c at the level.Comment: 23 pages, 14 figure
Unobtrusive and pervasive video-based eye-gaze tracking
Eye-gaze tracking has long been considered a desktop technology that finds its use inside the traditional office setting, where the operating conditions may be controlled. Nonetheless, recent advancements in mobile technology and a growing interest in capturing natural human behaviour have motivated an emerging interest in tracking eye movements within unconstrained real-life conditions, referred to as pervasive eye-gaze tracking. This critical review focuses on emerging passive and unobtrusive video-based eye-gaze tracking methods in recent literature, with the aim to identify different research avenues that are being followed in response to the challenges of pervasive eye-gaze tracking. Different eye-gaze tracking approaches are discussed in order to bring out their strengths and weaknesses, and to identify any limitations, within the context of pervasive eye-gaze tracking, that have yet to be considered by the computer vision community.peer-reviewe
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